ARTICLE
Figure 3. Limited space available for a standard engine single PTO can cause installation problems for hydraulic pumps. A solution is to use a pump that allows for larger displacements to be used in tight areas or employ two smaller pumps in a tandem / through drive package. equipment typically does not follow a pre-existing drive chassis and is designed for a specific machine purpose or activity. This allows the designers to work with a blank canvas for providing rotational power for pumps. Options that are typically used in these applications are: engine flywheel case coupling, engine crankshaft, belt / pulley, single or multi-pad PTO’ s, and pumps with built-in through drives. Similarly to on-highway applications, there is not one single method that is better than another, but there are design considerations for each method.
Some pump manufacturers offer engine flywheel mounts for their pumps which allow a direct coupling to the diesel engine. Most of these purposed pumps are in the high-pressure category, such as the Bosch Rexroth A11VO and A8VO( Figure 2), and offer installation space savings for applications. These are usually found in machines that use the hydraulics system as their only means to perform work, like excavators and feller bunchers. In these applications the engine power does not have to drive an axle, mechanical transmission or cardan shaft, allowing the space saving installations.
There are many times when the pump must be located in a different area of the application due to space constraints around the engine and machine frame. In these instances, an engine crankshaft can be used to couple the pump to the mechanical drive of the engine. For this type of mounting / coupling, it is important to monitor the angle and balance of the connection method to the pump to avoid undesired bending forces of the pump shaft. The pump drive shaft must be parallel to the engine crank shaft. Otherwise, an oscillation will be introduced to the pump drive speed which can eventually destroy the pump. Consult the pump manufacturer for the amount of allowable bending and axial forces the pump is designed to accommodate or to find ways to avoid the impact to the pump.
Belt and pulley systems offer an alternative to PTO driven methods. These are typically seen when access to the engine PTO is obstructed or when there is limited area around the engine. A design consideration for this type of input is the amount of horsepower that can be transmitted to the pump via the mechanical belt drive as well as monitoring the bending moments with axial and radial loads on the input shaft. These conditions usually limit the maximum possible power transmission and therefore pump size.
As discussed earlier, the limited space available for a standard engine single PTO can cause installation problems for hydraulic pumps. Depending on the desired displacement of the pump, the installation space claim for the pump may prevent an easy mounting to the engine PTO. The result is that the manufacturer may need to utilize spacers or other costly add-ons to allow for larger displacement pumps to be mounted. Consult your pump supplier to see if they offer any space saving options for these situations that may allow for larger displacements to be used in tight areas.
The Bosch Rexroth medium-pressure open loop pump, A10VNO( Figure 3), offers a solution in these types of situations where a compact unit with high displacement is needed for small installation spaces. Another idea sometimes utilized is to employ two smaller pumps in a tandem / through drive package, which when built up together are smaller in diameter, but become significantly longer.
Multi-pad PTOs offer the largest amount of flexibility for applications requiring multiple pumps. If you have multiple pumps that will need to operate at different input speeds, a multi-pad PTO typically can offer different output speeds by changing the internal gear ratios for each pad.
26 Global MDA Journal may 2018